Thank you, Nikki, for the response.
Disappointed that there is apparently no 'switch' to make custom properties 'stay there' when I insert a block.
However, block attributes may accomplish my goal, which is simply discovering how many of what kind of fastener (in this case) my contraption requires. I hadn't examined the 'multiple properties' aspect of block attributes; this may suffice for my limited requirement.
I've not played with the connection pallet at all; a quick reading of the user guide page doesn't tell me how the data is formatted to 'attach' to the object in the drawing. I'm imagining a spreadsheet, for example, with columns like 'head-type', 'thread', 'length', etc. Would I define a block, say a "SHBH 1/4-20 x 1", open the connection pallet, then assign a key field to the block? Can you point me to a discussion of the connection pallet that might help me see more clearly how it's used?